This invention relates to the art of making zipper equipped plastic bags and is more particularly concerned with a new and improved bag, material for making such bag, and a method and apparatus.
Plastic bags equipped with zippers integrally extruded therewith are exemplified in U.S. Pat. No. Re. 28,959. Integral extrusion of the thin bag film and the greater cross-sectional mass of the zipper profiles presents manufacturing problems, in particular having to do with the speed of manufacture. Increased production and the consequent manufacturing economies are important in what has become a very competitive market. Therefore, there is a constant effort toward improving and lowering the cost of production.
U.S. Pat. No. 3,543,343 discloses another example of integrally extruded profiles on a tubular film. In addition, this patent discloses equipping a freshly extruded tubular film with separately prefabricated complementary fastener profile strips. The integrally extruded profiles have the disadvantages already described in connection with U.S. Pat. No. Re. 28,959. Attachment of individual fastener strips is a complicated matter, and there is also the problem of attaining a reasonable degree of accuracy in alignment of the individually attached zipper strips.
In addition, U.S. Pat. No. 3,543,343 discloses the feature of fixing in the top fold of the bag material, separate from the integral zipper film structure, a tear thread or string. No indication is given as to how the end of the tear string is to be manipulated for opening a bag.
U.S. Pat. No. 4,101,355 discloses the fusion or adhesive attachment of zipper strips which carry complementary profiles which are adapted to interlock upon folding of the strips along a central fold line. However, this disclosure teaches securing all of the base or the base material on both sides of the profile, i.e. the lateral side flanges of each strip, to the bag film material.
U.S. Pat. No. 4,341,575 shows a similar arrangement as in U.S. Pat. No. 4,101,355 but is limited to attachment of the entire base of the zipper strip, including lateral side flanges, to the bag film.
U.S. Pat No. 4,430,070 discloses the securing of minor area of each of the base portions of the zipper strips directly back of the profiles thereof, whereby there can be a hinging of the profiles at the inner side of the bag. Each of the complementary zipper strips is independently attached to the bag body film spaced from the open end of the bag.